Gas springs are widely used to partly or totally counterbalance the engine compartment hoods, trunk lids, rear windows and tailgates of passenger cars, station wagons, and vans to facilitate opening them and to hold them open at a nearly or fully open position. It is well-known that the force outputs of gas springs vary considerably with the temperature of the gas—at low temperatures the gas spring produces a force that can be very much lower than the force produced at high temperatures. It is necessary, therefore, to design a gas spring so that it produces a sufficient force to hold open the hood, tailgate or the like (hereinafter referred to as the “load”) at a suitably selected low temperature. Ordinarily, gas springs are designed to provide a force of from about one to about five pounds over the load in the hold-open position of the load at the low temperature. At high temperatures, the hold-open force may increase by as much as 50 pounds, which means that the force required to move the load toward closed from the hold-open position (the “handle load”) can be more than 50 pounds.
In addition to the problem of wide variations in the handle load as a function of temperature, the counterbalancing force exerted by the gas spring on the load at all positions of the load between closed and open varies widely with temperature. In cold weather, the gas spring force exerts a considerably lower counterbalancing force on the load than at high temperatures. Depending on the geometry of the gas spring/load system, the user may have to exert a relatively large force on the load during part or all of the movement of the load from closed to fully open in cold weather. In hot weather the gas spring force may move the load from closed to open without the intervention of the user under a relatively high opening force and at a relatively high speed, which can sometimes be disconcerting to an unwary user or can damage the load if there is an obstruction that prevents the load from fully opening.
Gas springs have an inherent problem when used to lift or hold open any flap, gate or hatch across the wide range of temperatures experienced in a normal operating environment. Due to the proportional effect of decreased temperature decreasing gas pressure in a known volume, at cold temperatures gas springs provide a reduced lift or extension force.
To offset this effect, a temperature compensating valve assembly (TCV assembly) is assembled into the gas spring body. The temperature compensating valve separates the gas chamber of the gas spring into two separate pressure chambers. When the valve is closed, for example at temperatures above 4° C., the gas spring functions only using a main pressure chamber. The gas spring provides output force based on the mass of gas and volume contained within the main pressure chamber.
At cold temperatures, for example below 4° C., the valve opens, allowing the gas spring to operate and provide an output force based on the volume of gas in the main pressure chamber and an additional volume. The additional volume is contained in a secondary pressure chamber. The secondary pressure chamber provides an increase in output force due to the inverse proportionality of pressure and volume.
A previously developed TCV assembly is shown in FIGS. 1A and 1B which is constructed of machined aluminum. Three O-rings 1, 2, 3 are used in the assembly. The O-ring 1 seals the valve in the gas spring tube body to provide separation for the two pressure chambers. Another O-ring 2 seals the valve spring in the “closed” position 200. Finally, the third O-ring 3 provides compression of the valve spring and prevents noise and rattling in the “open” position 300.
A bimetallic valve spring 4 is used to actuate the valve at a specific temperature range. The spring is disk-shaped, and seals the valve at temperatures above 4° C. by pressing against an O-ring 2 seal. Below 4° C., the spring disengages the O-ring 2 seal and allows gas to pass through the valve. The bimetallic spring 4 is held in place by means of a compression O-ring 3 that is retained by cold forming a lip on the valve body. Different types of bimetallic springs 4 may be used. The temperature at which the different bimetallic springs 4 respond may be lower or higher than 4° C.
The TCV assembly of FIGS. 1A and 1B is composed of a one-piece machined aluminum assembly that holds the bimetallic spring in place and is sealed after manufacturing. It is difficult to perform maintenance after manufacturing. And it is also difficult to replace the bimetallic spring should it need replacing. There are also too many components, including three O-rings in the TCV Assembly, making manufacture complex and expensive.
There is a need to improve the functional characteristics of the TCV assembly. There is a need to reduce the number of components needed to construct the TCV assembly and to reduce the complexity of the assembly. There is also a need to improve the materials used to make the TCV assembly stronger and to improve the construction method. There is also a need for a TCV assembly that is easy to perform maintenance on.